Turbulence-driven anisotropic electron tail generation during magnetic reconnection

Abstract

Magnetic reconnection (MR) plays an important role in particle transport, energization, and acceleration in space, astrophysical, and laboratory plasmas. In the Madison Symmetric Torus reversed field pinch, discrete MR events release large amounts of energy from the equilibrium magnetic field, a fraction of which is transferred to electrons and ions. Previous experiments revealed an anisotropic electron tail that favors the perpendicular direction and is symmetric in the parallel. New profile measurements of x-ray emission show that the tail distribution is localized near the magnetic axis, consistent modeling of the bremsstrahlung emission. The tail appears first near the magnetic axis and then spreads radially, and the dynamics in the anisotropy and diffusion are discussed. The data presented imply that the electron tail formation likely results from a turbulent wave-particle interaction and provides evidence that high energy electrons are escaping the core-localized region through pitch angle scattering into the parallel direction, followed by stochastic parallel transport to the plasma edge. New measurements also show a strong correlation between high energy x-ray measurements and tearing mode dynamics, suggesting that the coupling between core and edge tearing modes is essential for energetic electron tail formation.

Bayesian inference applied to electron temperature data: computational performances and diagnostics integration

“…The detection and characterization of slideaway and runaway electron populations play an important role in both physics comprehension and technical failures mitigation. For instance, the features of electron distribution function (EDF hereafter) are linked to energy transport and pedestal dynamics [12] and affect self organizing processes such as RFP dynamo [7], reconnection events [3,9] and so on. Detection on suprathermal features in the EDF has been performed via electron cyclotron emission and X-ray spectroscopy [14].…”

Acceleration of charged particles to extremely large energies by a sub-Dreicer electric field

“…Surprisingly, energetic charged particles have been observed for decades in laboratory experiments, [1][2][3][4][5] solar flare events, [6][7][8][9][10] and astrophysical jets. 11,12 Despite the scales of these different structures spanning 22 orders of magnitude in length and 20 orders of magnitude in time, 13 they have certain critical similarities, namely, (i) charged particles are accelerated to energies orders of magnitude larger than thermal, (ii) the process is transient, (iii) magnetic fields and electric currents are involved, and (iv) the energization appears to be associated with some sort of instability.…”

Transport equations in magnetized plasmas for non-Maxwellian distribution functions

“…6,7 In tokamak plasmas, long-tail electron distributions have been observed over the whole plasma column (edge, confinement region, and core) and related to different mechanisms and instabilities, such as magnetic reconnection, high-energy ions, non-local electron transport, neutral ionization, internal kink modes, sawtooth instabilities, electron fishbones, and plasma heating. [8][9][10][11] In particular, bi-Maxwellian distribution functions, an empirical model for long tail distributions used in the same context of the j-distributions in space plasmas, were fitted to the experimental data in the plasma edge during Ion Cyclotron Resonance Heating (ICRH) and Neutral Beam Injection (NBI) experiments. 12,13 In order to introduce non-thermal effects in the Boltzmann-based models, alternative fluid equations approximating different long-tail distribution functions by a series of Maxwellians, with the coefficients of proportionality determined by numerically fitting the experimental data, have been lately considered, especially in numerical simulations.…”